In pneumatic grinding tools, compressed air provides power to the pneumatic tool to drive the pneumatic motor to rotate the pneumatic tool's shaft which couples to the grinding material. Thus, the grinding material at the end of the shaft can rotate and do the grinding job. Generally, the grinding materials on the market can be divided into at least the grinding brushes and the grinding wheels. The grinding brush has a flexible collar and metal bristles radially project outwards from the collar. Usually, the collar has a thickness of about 2.0 mm. Besides, according to the assembly way, there are two methods to install the grinding material on the pneumatic tool. One is that the grinding material itself has a fixing element at the center thereof to engage with the shaft. In other words, the grinding material and the fixing element are fabricated into a one-piece part. The other is that the grinding material has no built-in fixing element but needs a fixing element in order to install it to the shaft. In other words, the fixing element is separated from the grinding material and can be repeatedly used. This shows that if to have the separation type grinding materials installed firmly on the shaft, a fixing device for holding the grinding materials is needed. The present invention relatives to a separation type grinding brush, which also needs a separated fixing device. Therefore, only the prior arts of the separation type grinding materials will be discussed below.
A U.S. Pat. No. 5,386,608 (and a corresponding Germany patent DE4205265C1 of the same inventors) disclosed a “Rotary Brush Assembly”, which comprises: a brush and a brush holder. The brush is used in surface treatment. The brush holder has a cylinder, and a plurality of flanges radially extends outwards from the cylinder, and a retaining tongue extends axially from each flange. The brush has a flexible collar, and bristles radially project outwards from the collar. The collar also has bristle-free zones. The radially-extending flanges, the axially-extending retaining tongues and the cylinder jointly form a cage-like structure having a radial gap and an axial gap. The outer diameter of the cylinder is smaller than the inner diameter of the collar. The radial gap between the cylinder and the axially-extending retaining tongue is a multiple of the thickness of the collar. The length of the cylinder is greater than the width of the collar. The bristle-free zones are in fact loosely accommodated in the gaps. When the brush rotates, the part of brush collar whereon the bristles projected at between the retaining tongues will bulge in an appearance like three leaves of shamrock.
From the above description, it is known that the retaining tongues apply force to the bristles to drive the annular brush to rotate. In such a case, the brush collar and bristles would receive the force unequally. Thus, the bristles are apt to be distorted and damaged, and the durability of the brush is shortened. The abovementioned shamrock-like bulged bristles are due to the flexibility of the collar. Besides, the bristle-free zones are in fact loosely accommodated in the cage-like structured brush holder. Therefore, during usage, the entire annular brush moves and vibrates up and down, left and right, back and forth. Then, the surface of the cylinder will be persistently impacted and abraded by the bottom of the bristles (the bristles' metal bottom which fixed on the brush band), which will damage the holder and shorten the durability. As the bristles also vibrate and move up and down, left and right, back and forth, it is hard for the user to grind straight ground strips precisely. Furthermore, because the durability of the brush assembly is shortened by the up and down, left and right, back and forth displacements, and because the grinding quality and efficiency is degraded by the same reason, the prior art proposed by the Germany patent DE4205265C1 still has much room to improve.